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Thermodynamic cycle analysis of decarbonized combined cycle using Ammonia as fuel and working fluid
Yerim An and Jungsoo Park
The objective of this study is to evaluate the thermodynamic performance of a Brayton–Rankine combined power cycle fueled by ammonia (NH3), a carbon-free energy carrier of increasing interest, which is employed as both the fuel for the Brayton cycle and the working fluid for the bottoming Rankine cycle. The configuration consists of a Brayton cycle in which air serves as the oxidizer for ammonia combustion, with the resulting combustion-gas mixture acting as the turbine working fluid, coupled with a Rankine cycle with ammonia as the working fluid. The Rankine cycle evaporator is powered by the Brayton cycle exhaust gas to maximize waste-heat recovery. The enthalpy, entropy, and exergy of each component were assessed using the first and second laws of thermodynamics. The overall energy and exergy efficiencies of the system were subsequently evaluated. The results indicate that the standalone Brayton cycle exhibited a thermal efficiency of 13.78%, while integration with the Rankine cycle enhanced the overall thermal efficiency to 15.65%, representing an improvement of approximately 1.87 percentage points. Similarly, the exergy efficiency increased from 12.88% to 14.63%, highlighting the potential for enhancing energy quality through waste-heat recovery. This study provides a theoretical foundation for improving the performance of ammonia-fueled carbon-free power-generation systems and is expected to inform the design of next-generation thermal energy systems.
Keywords: Brayton cycle, Rankine cycle, Ammonia, Combined cycle, Waste heat recovery, Exergy analysis, Carbon-free fuel, Parametric analysis
DOI: 10.32908/hthp.v55.2107